1. Field of the Invention
The invention relates in general to a system and a method for effectively removing entrained gas bubbles from a feed material system for an ink-jet material dispensing system. The system and method is designed to completely remove entrained gas bubbles before the feed material is fed to an ink-jet print head.
2. Description of the Prior Art
Recently, several new technologies have been developed for the rapid creation of models, prototypes, and parts for limited run manufacturing. These new technologies can generally be described as solid freeform fabrication, herein referred to as “SFF”. Some SFF techniques include stereolithography, selective deposition modeling, three-dimensional printing, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, and the like. In SFF, complex parts are produced from a modeling material in an additive fashion as opposed to conventional fabrication techniques, which are generally subtractive in nature. For example, in conventional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to targeted locations, typically layer by layer, in order to build a complex part.
SFF technologies typically utilize a computer graphic representation of a part and a supply of a build material to fabricate the part in successive layers. SFF technologies have many advantages over the prior conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts and can quickly produce limited numbers of parts in rapid manufacturing processes. They also eliminate the need for complex tooling and machining associated with the prior conventional manufacturing methods, particularly when creating molds for casting operations. In addition, SFF technologies are advantageous because customized objects can be produced quickly by processing computer graphic data.
One category of SFF that has emerged is selective deposition modeling, herein referred to as “SDM”. In SDM, a build material is physically deposited in a layerwise fashion while in a flowable state and is allowed to solidify to form an object. In one type of SDM technology the modeling material is extruded as a continuous filament through a resistively heated nozzle. In yet another type of SDM technology the modeling material is jetted or dropped in discrete droplets in order to build up a part. In one particular SDM apparatus, a thermoplastic material having a low-melting point is used as the solid modeling material, which is delivered through a jetting system such as those used in ink jet printers. One type of SDM process utilizing ink jet print heads is described, for example, in U.S. Pat. No. 5,555,176 to Menhennett, et al.
Because ink jet print heads are designed for use in two-dimensional printing, special modifications must be made in order to use them in building three-dimensional objects by SFF techniques. This is generally because there are substantial differences between the two processes requiring different solutions to different problems. For example, in two-dimensional printing a relatively small amount of ink is jetted and allowed to dry or solidify with a significant interest being given to print resolution. Because only a small amount of material is jetted in two-dimensional printing, the material reservoir for the liquid material can reside directly in the ink jet print head while providing the ability to print numerous pages before needing to be refilled or replaced. In contrast, in SDM utilizing an ink-jet print head, a normally solid material, such as a photo curable, thermoplastic, or wax material, is frequently employed and often must be heated to a flowable state in order to be jetted, and then allowed to solidify. Furthermore, in SDM dispensing resolution is not as critical as it is in two-dimensional printing. This is generally because, for each targeted pixel location, the amount of material to be jetted in SDM techniques is substantially greater than the amount to be jetted in two-dimensional printing techniques. For example, it may be required to deposit six droplets on a particular pixel location in SDM compared to just one or two droplets in two-dimensional printing. Although the targeting accuracy may be the same, the actual resolution achieved in SDM techniques is generally somewhat less than in two-dimensional printing because the six droplets dispensed may droop or slide towards adjacent pixel locations.
The differences mentioned above are significant and create a number of problems to be resolved. For instance, the amount of material deposited in inkjet based SDM techniques, both in volume and in mass, can be so substantial that it is generally considered impractical to mount a reservoir directly on the ink jet print head to hold all of the material. Thus, it is typical in most SDM systems to provide a large reservoir at a remote location from the print head that is in communication with the ink print head via a material delivery system having a flexible umbilical cord. However, the large container and umbilical cord must be heated to cause at least some of the build material to become or remain flowable so that the material can flow to the dispensing device. Undesirably, start up times are longer for SDM techniques using ink jet print heads than in two-dimensional printing with ink jet print heads due to the length of time necessary to initially heat the solidified material in the large remote reservoir to its flowable state. In addition, a significant amount of energy is required to maintain the large quantity of material in the flowable state in the reservoir and in the delivery system during the build process. This undesirably generates a significant amount of heat in the build environment.
Another problem that is unique to SDM techniques is that the layers being formed must be shaped or smoothed during the build process to establish a uniform layer. Normalizing the layers is commonly accomplished with a planarizer that removes a portion of the material dispensed in the layers. One such planarizer is disclosed in U.S. Pat. No. 6,270,335 to Leyden et al. However, the planarizer produces waste material during the build process that must be handled. By-product waste handling systems for dealing with the aforementioned waste stream from an SDM process is described in U.S. patent application Ser. Nos. 09/970,956, and 10/625,745, both from 3D Systems, Inc., and both incorporated herein by reference.
Whether the system is a SDM type system, the three dimensional printing type, or a more conventional two dimensional ink-jet system, an ongoing problem with these systems is the possibility of gas bubbles introduced in the feed material systems entering the print head of an ink-jet dispensing system. Once such gas bubbles reach the print head the performance of the jets is impaired and recovery is difficult. In an SDM type of system, where different build and support materials are employed, the problem is compounded. Often the filter screen in the ink-jet print head becomes blocked with gas bubbles preventing the flow of build or support material to the orifices or the orifices themselves become blocked with gas bubbles. This problem often requires a visit from an experienced field service engineer to carefully disassemble the system to remove gas bubbles, or replacement of the print head if purging of the trapped gas bubbles is not successful. A number of design approaches have been used to avoid this issue. They usually involve careful design of the feed containers to help eliminate initial incorporation of gas bubbles in the feed material or periodic vacuum purging of the print heads. But this problem continues to be an issue.
The problem of such gas bubbles is particularly difficult in some material systems because more than one type of gas bubble can be present in the system. Particularly it can often happen that both large, easily observable macro gas bubbles are seen in these systems and there can be innumerable small and almost invisible to the naked eye micro gas bubbles. These small-scale bubbles, which behave in a less buoyant manner are sometimes easily entrained in the liquid and will not readily rise to the top of any liquid flow or in any vessel. Yet these micro bubbles can accumulate in the filters of the ink-jet heads and eventually either plug the filters or breakthrough the filters and plug the individual jets of the ink-jet head.
These and other difficulties of the prior art are overcome according to the present invention by providing a new, simple gas bubble remover in an ink-jet dispensing system that ensures that gas bubbles in the system, whether introduced in the feed containers, or introduced by leakage, and whether macro or micro bubbles are effectively removed from the material feed stream immediately before it enters the ink-jet print head.